In relation to an electrophotographic color printer, the so-called tandem type color printer having parallelly arranged photosensitive drums corresponding to yellow, magenta, cyan and black respectively is in the process of forming the mainstream.
Tandem type color printers include that having a tandem type photosensitive unit formed by collectively retaining four photosensitive drums with a pair of side plates and detachably mounted on a main body casing.
The photosensitive drums include cylindrical drum bodies and drum shafts arranged along the axial directions of the drum bodies. The pair of side plates are fixed to beams provided on both sides in a direction orthogonal to the opposed direction thereof (a direction orthogonal to the drum shafts) respectively. Four shaft holes are formed in each side plate at regular intervals in the arrangement direction of the photosensitive drums. Both end portions of the drum shafts of the photosensitive drums are inserted into the shaft holes of the side plates respectively, so that the four photosensitive drums are positioned to be precisely arranged at a constant pitch.
The black photosensitive drum is more frequently used as compared with the remaining three photosensitive drums, and hence has a short life. Further, the drum body of any photosensitive drum may be damaged, depending on handling of the tandem type photosensitive unit. In order to ensure excellent image quality, the photosensitive drum must be exchanged for a new one when the same is used up or the drum body thereof is damaged.
In the structure of the aforementioned color printer, however, the drum shaft of each photosensitive drum is inserted into the shaft holes of the side plates. If any photosensitive drum must be exchanged for a new one, therefore, this photosensitive drum cannot be detached from the pair of side plates in the state fixed to both beams. In this case, therefore, at least one of the side plates must be dismounted (detached) from both beams for exchanging the photosensitive drum for a new one and the drum shafts of all photosensitive drums must be thereafter inserted into the shaft holes of the side plate, which in turn must be fixed to the beams again. Thus, the operation for exchanging the photosensitive drum is time-consuming.